1. Technical Field
The present invention relates to printing apparatuses and printing methods.
2. Related Art
In inkjet printers or the like, a print image is printed on paper by alternately repeating a dot forming process in which dots are formed on paper by ejecting ink droplets from a plurality of moving nozzles, and a carrying process in which paper is carried in a carrying direction, thereby arranging a plurality of dot rows (raster lines) in the carrying direction on paper. In the head of an inkjet printer, nozzle rows for respective colors are provided for ejecting ink droplets of each color (JP-A-2001-96771).
When a dot is formed by superimposing two or more colors of ink droplets, the color appearance of the dot varies depending on the landing order of the ink droplets. The reason for this is as follows. The ink droplet that first lands on paper spreads over a broad area on the paper to be soaked by the paper. The ink droplet that subsequently lands on the paper overlaps the first ink droplet and spreads over a smaller area than the initial ink droplet. The color of the ink droplet that first lands on paper is developed in a more conspicuous manner than the ink droplet that subsequently lands on paper.
When bidirectional printing is performed, since the landing order of two or more colors of ink droplets that form a dot varies between a dot formed in the forward pass printing and a dot formed in the return pass printing, the color appearance of these dots varies. When raster lines formed in the forward pass printing or raster lines formed in the return pass printing are formed consecutively lined up, such variance in the color appearance of dots becomes conspicuous, and may generate band-shaped unevenness in color.